Thermal evaluation of the use of porous ceramic plates on ventilated façades—part II: Thermal behavior

The effects of porous ceramic plates on the thermal behavior of ventilated façades were evaluated, and the results are presented herein. Thermal behavior in a ventilated façade of specimens containing 40 wt% of lime mud and a firing temperature of 1100°C was evaluated and compared with a commercial porcelain ceramic tile, which was the reference material. An experimental apparatus was designed to evaluate the thermal performance of the studied ventilated façades. The results revealed that the ventilated façade composed of the studied porous ceramic tiles produced a greater reduction in temperature between the external environmental and the interior of a box representing a building (ΔT5) of 65.7°C, compared with the façade composed of the commercial porcelain ceramic tiles (ΔT5 = 56.0°C) and even the traditional façade (ΔT5 = 49.1°C). Thus, porous ceramic tiles based on byproducts are promising candidates for ventilated façade systems.     

Effects of micro-sized mullite on cristobalite crystallization and properties of silica-based ceramic cores

Silica-based ceramic cores are extensively used in investment casting process, during which they must exhibit sufficient flexural strength and deformation resistance. In this study, micro-sized mullite was used as an additive to silica-based ceramic cores to optimize their high temperature properties. To investigate the effects of micro-sized mullite on cristobalite crystallization, mechanical and thermal properties of silica-based ceramic cores, ceramic cores with different amounts of micro-sized mullite were fabricated. The XRD results showed that additional micro-sized mullite diminished the crystallization of cristobalite at high temperatures, primarily caused by the mullite related compressive stresses on the surface regions of fused silica particles. Three-point bending tests and SEM results showed that micro-sized mullite had a more significant effect on the flexural strength of ceramic cores compared with conventional additives. Particularly, the fracture mechanism of silica-based ceramic cores had been changed from intergranular fracture into a mixed fracture consisting of both intergranular and transgranular fracture. The mechanical and thermal properties of ceramic cores were all reduced slightly as the mullite content exceed 4.6 wt%. Hence, to optimize the properties of silica-based ceramic cores, the micro-sized mullite content should not exceed 4.6 wt%.     

Influences of mullite fibers on mechanical and thermal properties of silica-based ceramic cores

Mullite fibers composite silica-based ceramic cores were successfully prepared by injection molding. The effects of mullite fibers on the mechanical and thermal properties of ceramic cores were investigated. The results indicated that the linear shrinkage was significantly decreased and the porosity was gradually increased with the increase of mullite fibers. In addition, the flexural strength for the room temperature and the simulated casting temperature of 1500°C was increased to a maximum value when the content of mullite fibers was about 1 wt.%, and then decreased with the increase of mullite fibers. The mullite fibers of 1 wt.% presented excellent mechanical properties with a linear shrinkage of .65%, a porosity of 6.96%, and a flexural strength of 17 MPa at room temperature and 34.83 MPa at the simulated casting temperature of 1500°C. Besides, the change in microstructure and properties in various contents of mullite fibers were analyzed.     

陶瓷/金属钎焊与扩散连接的研究现状

工程陶瓷由于具有优异的综合性能,在许多领域得到广泛应用,但其加工性能差,通常需要与金属组成复合结构.实现陶瓷与金属之间的可靠连接是推进陶瓷材料应用的关键,钎焊和扩散连接被认为是陶瓷/金属连接中较为适合的方法.文中对近年来国内外陶瓷/金属钎焊和扩散连接技术领域的研究现状进行了综述,认为活性金属钎焊和部分瞬间液相连接发展比较成熟,部分瞬间液相连接充分结合了活性钎焊和固相扩散连接两者的优点,将成为未来陶瓷/金属连接的发展方向.     

纳米粉及添加剂对压电陶瓷材料性能的影响

采用高能球磨法研磨出PZT-5纳米粉料，添加外购的纳米有机添加剂，按照传统的固相工艺法制备出了压电陶瓷材料，研究分析纳米粉料和纳米有机添加剂对压电陶瓷性能的影响。通过测试分析可以看出，纳米压电粉料与纳米有机添加剂的综合作用，降低了材料的烧结温度、相对介电常数εr,Qm值和以d31，提高了压电应变常数d333，从而压电电压常数g33、gh、dh成倍提高，这些对制作宽带、高灵敏度的换能器是很有好处的。     

Conductivity enhancement in transparetn ZnO films via Al-dopping produced by CW-CO2 laser-induced evaporation

Highly conductive transparent aluminium-doped ZnO (ZnO:A1) films were successfully deposited by CW-CO₂ laser-induced evaporation. Optimisation of evaporation parameters was based on laser power, substrate temperature, O₂ partial pressure in the vacuum chamber and amount of Al in the ZnO source pellet. ZnO:A1 films with an electrical resistivity as low as 6.6 × 10⁻²Ω·cm and an optical transmission of 80% at 500nm were obtained at laser power of 15 W, substrate temperature of about 200°C, O₂ partial pressure of 6—7 × 10⁻⁴ Torr and 5wt.% Al. Conductivity of ZnO films can be increased one order via Al-doping in ZnO films. The films obtained by laser-induced evaporation have compared quite favorably with the high quality films obtained by sputtering.     

爆炸压实烧结ITO陶瓷靶材的实验研究

通过爆炸压实烧结纳米ITO粉末制备了ITO陶瓷靶材，结果表明爆炸冲击压实在靶材的后续烧结密实过程中起到了促进作用，它与常规的加压烧结相比，具有操作简单，设备要求低等很多优点。经过爆炸压实的烧结靶材具有细小的晶体颗粒，比商业靶材的晶粒度小约1个数量级。     

陶瓷与金属特种焊接技术的开发与应用

介绍了近年来发展的陶瓷与金属的焊接技术，并对其焊接工艺特点及应用情况进行了分析与总结。     

铸件内析出性气孔形成及演化的直接观察与分析

采用透明模型合金实时观察了铸件析出性气孔的形成发展,结果发现,纯物质凝固时,析出性气孔的产生发生于凝固型壳形成之后,随着凝固自型壁向中心凝固,呈现自周边向中心的气条生长。对于合金凝固,析出性气孔在凝固基本完成之后伴随着热裂及缩松的发生开始产生,呈现一定的偏聚现象。浇注前熔体过热度的提高将使析出性气孔更加密集,铸型和环境温度的降低有利于降低气孔的数量及分布范围,采用真空除气,可有效地抑制析出性气孔的产生和热裂缩松缺陷的形成。